This invention relates to a method of concentrating minerals which when mined are recovered in plate-shaped form. More particularly, this invention pertains to an improved, highly efficient process for concentrating and sorting plate-shaped minerals such as vermiculite and other micas which are recovered in admixture with non-plate like gangue materials such as rocks, etc.
Vermiculite is a mineral of micaceous origin having the very desirable property of exfoliating or expanding when heated to a state many times its original size and density to form a lightweight, inert, highly porous aggregate material of many uses. As mined, the mineral is recovered in its characteristic "plate-like" shape in association with gangue rocks and minerals such as feldspar, quartz, diopside, etc.
Many processes for concentrating or for separating vermiculite from other constituents found in vermiculite ore are described in the art. Such procedures range from simple screening with vibrating screens having varying sized and shaped openings to relatively more sophisticated processes involving treatment with chemicals, etc. or combination of such.
For many years, the processes commercially applied have proceeded with an initial separation of the mined vermiculite ore into "coarse" and "fine" fractions, with subsequent markedly different treatment of the sized fractions thereafter. The "coarse" fraction was usually concentrated by screening using various types of screen cloth on vibrating screens. Treatment of the "fine" fraction utilized conventional "froth flotation" techniques to recover a concentrate rich in vermiculite.
One type of screen employed in the past to concentrate the coarse vermiculite ore fraction was the "slot" screen. This screen had openings which were in the form of slots dimensioned such that only plate-like particles could pass edgewise therethrough. This screen however was subject to "blinding", that is, blocking up of the slots by particles which were not exactly oriented or aligned with the slots. Also the degree of concentration obtained with this device depended upon the presence of more plate-like material in the feed than granular material, and in turn more of the plate-like material being vermiculite particles than non-vermiculite platelets.
The inefficiencies of the slot screen led to the substitution of the so called "plate" separator for the slot screen in the coarse vermiculite processing circuit. The plate separator consists of an inclined rubber covered plate with two adjacent discharge compartments located near the bottom end of the inclined plate, cone compartment being positioned further away from the plate than the other. The coarse feed is introduced to the top of the plate and allowed to travel freely down the incline. Rock and other unwanted constituents of the ore bounce off of the plate and into the discharge compartment located furthest from the board, while the plate-shaped vermiculite particles tend to adhere to the plate surface and drop into the closer discharge compartment.
The "plate" separator is simple in design with no moving parts. However, continuous adjustment of a discharge "splitter" located at the lower end of the inclined plate is required in order to compensate for the variances in feed rate and feed characteristics. Also, the plate separator is not so efficient as to produce a product rich enough to be a final concentrate, and thus is used only as a "rougher", generating a middling for further processing.